The invention relates to turbochargers in which a turbine of the turbocharger is driven by exhaust gas from a reciprocating engine. The invention relates more particularly to turbine housings that are divided into a plurality of substantially separate sections each fed by a separate exhaust system.
In multiple-piston reciprocating engines, it is known to design the exhaust system in such a manner as to take advantage of the pressure pulsation that occurs in the exhaust stream. In particular, it is known to employ what is known as “pulse separation” wherein the cylinders of the engine are divided into a plurality of subgroups, and the pulses from each subgroup of cylinders are substantially isolated from those of the other subgroups by having independent exhaust passages for each subgroup. To take best advantage of pulse separation, it is desired to minimize the communication or “cross talk” between the separate groups of cylinders. Accordingly, in the case of a turbocharged engine, it is advantageous to maintain separate exhaust passages all the way into the turbine of the turbocharger. Thus, the turbine housing into which the exhaust gases are fed is typically divided into a plurality of substantially separate parts.
There are basically two ways in which turbine housings have been divided: (1) meridional division, and (2) sector division. In a meridionally divided turbine housing, the generally annular volute or chamber that surrounds the turbine wheel and into which the exhaust gases are fed is divided into a plurality of passages in the meridional plane such that each passage occupies a full circumference and the passages succeed each other in the axial direction, such as shown in FIG. 4 of U.S. Pat. No. 4,027,994.
The present invention relates instead to sector-divided turbine housings. In a sector-divided turbine housing, the generally annular chamber is divided into angular sectors each of which occupies only a part of the circumference such that the passages succeed each other in the circumferential direction, such as shown in FIG. 2 of U.S. Pat. No. 6,260,358. That figure also shows guide vanes 12 that are positioned just radially inwardly of the chamber and guide the flow into the turbine wheel.